What you're seeing with your .243 shooting 2" high at 100 yards and then 6" high at 200 yards is a classic case of bullet trajectory physics — and it's likely down to one or both of the following setup factors.
1. Scope height over bore:
If your scope is mounted significantly higher than the bore (say, 1.75" or more), the barrel has to be angled upward relative to the line of sight to intersect the scope’s axis at your zero point. This means the bullet starts below the line of sight, climbs to meet it at the zero range, continues to climb at 100 yards (where you’ve zeroed 2" high), and continues rising beyond that — hence the 6" high impact at 200 yards. The steeper the angle between bore and scope, the more pronounced this climb will be.
2. Scope mount cant (rear mount higher than front):
If your rear scope ring or base is higher than the front — intentionally or due to a misalignment — it introduces additional cant to the scope. This setup is often used for long-range shooting to preserve elevation adjustment, but at shorter ranges it causes the barrel to be angled even more steeply upward relative to the scope. That exaggerated angle means the bullet continues to climb well past your initial zero.
3. Ballistic characteristics of the .243:
The .243 Winchester is a high-velocity, flat-shooting round. When zeroed to hit high at 100 yards, it’s still in its rising phase of trajectory at 200 yards. Depending on your load (bullet weight, muzzle velocity), the bullet may not reach its apex until somewhere between 250–300 yards. So if you’re zeroing for longer distances, this kind of rise is expected. However, 6" seems excessive to me, so would suspect one of the first two issues.